1. Technical Field
The present invention relates to a manufacturing method of a semiconductor device having the step of forming a thin film on a substrate, and a substrate processing apparatus suitably used in this step.
2. Description of Related Art
With micronization of a flash memory and reduction of an operation power for low power consumption, a tunnel oxide film is likely to be thinner. However, there is a risk of reducing reliability of a device due to insulation breakdown and a stress-induced leak current, while the tunnel oxide film is becoming thinner, and therefore an alternative technique having a floating gate type structure, being a conventional technique, has been requested. Among them, an insulation trap type structure gathers attention, which utilizes charge traps of a nitride layer such as a silicon nitride film (also called a SiN film hereinafter). This is because further micronization is realized by widening electric charge to a trapping medium, in a circumstance that a conventional gate type structure has a high sensitivity to a local defect of the tunnel oxide film and this is a main factor of interrupting further micronization. Further, there is no problem of electrostatic interference in this insulation trap type structure, and this is also a reason for gathering attention.
When a nitride layer formed on the tunnel oxide film is formed by an ALD (Atomic Layer Deposition) method and a CVD (Chemical Vapor Deposition) method, an extremely uniform thin film in terms of its characteristics can be formed. However, a time delay occurs in some cases for starting deposition of the thin film on a substrate surface. Such a time is called an incubation time. A nucleus forming process of performing island-like deposition on the substrate occurs during the incubation time, to thereby form irregularities in this nucleus forming process. Therefore, a film quality is sometimes different from a film formed after the nucleus forming process.
In the insulation trap type structure, when the film quality of a nitride film body, being the thin film formed on the tunnel oxide film, is different from the film quality in an interface between the nitride film and the tunnel oxide film, the electric charge is trapped by not only a nitride layer but also by the interface between the nitride layer and the tunnel oxide film, thus making it impossible to exhibit superiority of the insulation trap type structure. Control of the incubation time is necessary, from a viewpoint of improving the film quality of the interface between the nitride layer and the tunnel oxide film, being a base of film formation, and from the viewpoint of controlling the film quality.